Radio Frequency (RF) communication may provide long range communication for a plurality of stationary and moving nodes (stations). High Frequency (HF) RF may possess waveform qualities specifically suited for long range communication. In establishing a communication link between two nodes, traditional Automatic Link Establishment (ALE) techniques may generally support one hop (one point to one point) route communication link setup. For example, a one hop communication link may employ ALE to create a communication link between a HF node in San Francisco and a HF node onboard a distant ship sailing in the Indian Ocean.
Even though this one hop limitation does not hinder most of HF communication needs, it may be fatally disrupted during periods of atmospheric disruptions such as solar flares, nuclear events, and coronal mass ejections (CME).
In traditional systems, HF communication may be limited to air to ground, ground to ground, and ground to air communication. Airborne nodes are currently unable to communicate with each other even with positive RF connectivity.
Traditional HF operation also requires an operator to perform a link between the two points. The HF operator is needed since 1) a trained operator is needed to determine time of day, location, propagation conditions etc. required to setup an HF call; and 2) ALE techniques and HF waveform properties are distinct operations requiring intelligent human integration.
HF communication relies heavily on a RF transmission 1) transmitted from a surface or near surface station; 2) reflected by one or more layers of the atmosphere; and 3) received by the second surface or near surface station. During Solar Flares and CMEs 1) the D-layer of the atmosphere attenuation greatly increases; and 2) the E-layer becomes more refractive due to increased ionization densities. As a result, a signal may still reach the destination node with some level of attenuation and communication may still be possible. More likely during these disruptions, the signal is attenuated to a level that communication with the destination node is not possible.
One possible solution to this problem may include increased power at both transmitter and receiver. If the HF power amplifier at one or both locations had a spare power margin, power output may be increased to combat the effect of increased D-layer attenuation. Additionally, ALE may be employed to use higher frequencies that pass through the D and E layers much more easily. More likely, the E-layer is so ionized that the HF signal reflects off the E-layer and bounces back to earth preventing communication with the destination node.
Another possible solution may be to employ ALE to locate higher frequencies that pass through the E-layer to reflect off the F-layer. However, it is still very probable, even after increasing the HF power amplifier power output and going to a higher frequency, communication with the destination node will likely be impossible.
Nuclear explosions are man-made ionosphere disruptors which ionize the D-layer of the atmosphere to such an extent that HF communication may not be possible due to excessive increase in signal attenuation. The ionospheric disruption by a nuclear event may be temporary and confined to a radius of a few hundred miles. HF transmissions attempted through this disrupted area may be impossible during the ionization. As in the natural events, during the time after a nuclear event, there is a very high probability that ALE may not be able to find a direct one hop path between surviving HF communication nodes.
Sunlight also affects the layers of the atmosphere and thus, the reflective properties thereof. During the day, the increased attenuation due to sunlight radiation impacting the ionosphere may last for as long as 6 to 8 hours while during the night, the increased attenuation may last for up to 30 minutes after sunset. During normal movement of the sun, D-layer attenuation is locally present during daylight, with D layer locally disappearing during the night and the E-layer typically disappears (locally) during night time leaving only the F-layer.
In addition to natural and man-made disruptions to the atmosphere, HF communication may be limited by traditional ALE methods. Because propagation of RF signals at HF frequencies is complex and involves multiple variables including 1) receiver and transmitter locations with respect to the Sun, 2) the frequency, and 3) the Smoothed Sunspot Number. Conventional methods have utilized ALE protocols to find suitable frequencies allowing reasonable communication rates between two nodes.
Certain critical limitations of ALE in the past have continued into the current generation ALE. This weakness or flaw in current methods may include that ALE, as a function, is evoked under one of two conditions either: 1) to find a suitable frequency on which to communicate, or 2) after the communication link has degraded and failed, ALE is again evoked to find a new frequency upon which a new channel may be built. This frustrating degradation and failure causes a break in HF communication causing time delays and missed communication opportunities.
This paradigm of waiting until the link collapses continues to plague HF capabilities since each user knows with certainty that unless both the users and the Sun remains stationary, whatever link is being used will certainly fail during the period of transmission. Many users resort to more expensive space based methods of long range communication.
Some traditional line of sight (LOS) communication methods maintain a communication link by changing a frequency or a base transmitter before a signal may deteriorate to a point of failure. These LOS methods lack an ability to function in a Beyond Line of Sight (BLOS) network of prearranged nodes.
Therefore, a need remains for a relay-hop routing mechanism using advanced ALE via intermediate nodes to reach the end user. This novel approach where ALE and waveform is integrated may reduce or eliminate need for an operator and allow successful communication worldwide.